In a cylinder head gasket, sealing against the greatest pressures occurring during operation of the engine must be effected around a combustion chamber through-opening of the gasket. For this reason, a ring-shaped combustion chamber sealing element of the cylinder head gasket is provided there, which encloses the combustion chamber through-opening, and in the area of which, when the gasket is installed, the latter is pressed to the greatest extent between the engine component sealing surfaces of cylinder head and engine block, i. e., is subjected to the highest pressing forces.
During operation of a reciprocating-piston internal combustion engine, the engine component sealing surfaces delimiting the sealing gap between cylinder head and engine block (possibly including cylinder liners) will unavoidably become displaced relative to one another in the plane of the sealing gap, for example, when owing to the high gas pressure occurring in a cylinder during the ignition, the cylinder head and hence the cylinder head sealing surface arch somewhat and the pressure between the cylinder head gasket, on the one hand, and the engine component sealing surfaces, on the other hand, is reduced somewhat, albeit only for quite a short time in each case. The sliding movements of the two engine component sealing surfaces relative to one another are particularly large in the case of engines with a cylinder head made of a light metal alloy and an engine block made of gray cast iron (owing to the different thermal expansions of these two materials). From the two above-explained causes for these sliding movements of the engine component sealing surfaces it follows that these sliding movements acting on the cylinder head gasket are not identical in size in all areas of the sealing gap. If it is unavoidable that during operation of the engine, the engine component sealing surfaces will become displaced relative to one another also in the area of such a combustion chamber sealing element, above all, during the cyclically occurring, brief reduction in the pressing forces acting on the combustion chamber sealing element during ignition of a cylinder, the sliding movements of the engine component sealing surfaces, in particular of the cylinder head sealing surface, relative to the combustion chamber sealing element result in frictional wear, above all, at the cylinder head sealing surface, but possibly also at the engine block sealing surface and at the combustion chamber sealing element, which may result in failure of the gas sealing around a combustion chamber.
There is disclosed in FIG. 10 of DE-195 12 650-A1 of Elring Klinger GmbH a substantially metallic cylinder head gasket, the gasket plate of which comprises a single sheet steel layer extending over the entire gasket plate, with an edge portion of the sheet steel layer, which surrounds a combustion chamber through-opening of the cylinder head gasket, folded back onto itself so as to form a so-called fold flange ring of U-shaped cross section around the combustion chamber through-opening. Directly beside and radially outside of this fold flange ring there lie on the sheet steel layer three wire rings of circular cross section which are each closed within themselves and are concentric with one another and with the combustion chamber through-opening, and the diameter of these wire rings is somewhat larger than the sheet thickness of the sheet steel layer, so that they project somewhat over the fold flange ring. For this reason, when this known cylinder head gasket is installed, the largest specific surface pressures between the engine component sealing surfaces and the cylinder head gasket occur in the area of these wire rings. The wire rings are to serve to intercept the described sliding movements of the engine component sealing surfaces relative to one another, because upon occurrence of such sliding movements, which are in the order of magnitude of a few tenths of a millimeter, the wire rings can roll on the one engine component sealing surface, and sliding friction is thus to be avoided between the cylinder head gasket and the engine component sealing surface adjacent to the wire rings—on the side of the known cylinder head gasket opposite the wire rings, when the gasket is installed, the sheet steel layer carrying the wire rings is pressed against the other engine component sealing surface, and the inventors of this known construction assumed that frictional wear is avoidable there during operation of the engine if the engine component sealing surface pressed against the wire rings is displaceable without restraint relative to the cylinder head gasket and to the other engine component sealing surface. However, for the following reasons this known cylinder head gasket is not satisfactory in every respect: the wire rings, whose round cross section has a relatively small radius of curvature owing to the given dimensional relations, result in a relatively high specific surface pressure between the wire rings and the engine component sealing surface pressed against these, and during operation of the engine the wire rings can, therefore, cause plastic deformations of this engine component sealing surface. Furthermore, the wire rings are parts which lie loosely on the actual cylinder head gasket, which makes handling of the cylinder head gasket for the purpose of shipment and installation in the engine difficult. Finally, by way of a special design of the cylinder head gasket, the wire rings must be prevented during operation of the engine from becoming displaced in an undesired manner relative to the sheet steel layer carrying them. For this reason, stops were provided for the wire rings in radial direction in relation to the combustion chamber through-opening, namely, on the one hand, in the form of the fold flange ring directly surrounding the combustion chamber through-opening and, on the other hand, by a crown of tongues provided radially outside of the wire rings, which were bent out of the sheet steel layer and bent back onto the latter. Lastly, it will be pointed out that by reducing the number of wire rings, which is desirable in view of a reduction in costs, which is always aimed at, the above-explained problem (plastic deformation of the engine component sealing surface pressed against the wire rings) would be further aggravated, namely as a result of an increase in the specific surface pressure between the remaining wire ring or remaining wire rings and the engine component sealing surface pressed thereagainst.
The object underlying the invention was to so improve the above-explained known cylinder head gasket that the risk of wear occurring during operation of the engine on the engine component sealing surfaces and the cylinder head gasket is at least reduced.